Read the example below and think about the writer's tone. Running as a form of exercise is easy to do because it does not require any special equipment. You will need good shoes, but you may already have a pair that will work. Besides that, the only other thing you will need is a safe place to run. Often people run in their neighborhood or in a park. Others use a treadmill or run at a track, but any of these options, as long as they are safe, can provide a place to get an excellent workout.

How does the writer establish credibility through her tone?
A. by using colloquialisms and idioms
B. by adhering to the conventions of standard written English
C. by using a variety of sentence types and lengths
D. by using a mix of formal and informal language